This invention relates to an apparatus for controlling a robot. More particularly, the invention relates to an apparatus for controlling the movement of a robot which has a first drive axis for supporting motion of a robot member, such as an arm, hand, or the like, in a vertical direction, and one or more second drive axes for supporting motion of the robot member in a horizontal direction.
Generally speaking, in controlling the operation of a robot member as it performs, for example, a so-called pick-and-place movement for moving an object from a home position to another location, the object is first grasped and then moved. In moving the object, the robot member is first lifted in a vertical direction, hereinafter referred to as the "Z axis". The member is then moved horizontally in a lateral direction, hereinafter known as the "X-Y axes". Finally, the member is caused to descend, again moving along the Z axis. These motions are shown in FIG. 1(a) of the drawings. In conventional robot control systems which perform the aforesaid motions, there is a single movement control circuit which has a calculating function and the pick-and-place operation is divided into three steps, each successive step being performed after completion of the preceding step. Thus, after the ascending movement along the Z axis has accelerated the robot member and then decelerated it to a halt, the member is accelerated along the X-Y axes. When the movement along the X-Y axes has been subsequently decelerated and stopped, the process is again repeated for descending movement of the member along the Z axis.
The foregoing method of operating a robot member, such as an arm or hand, is time consuming. In order to reduce the time of operation, it is desirable to speed up the operation. However, increases in rates of acceleration and in velocities of movement beyond reasonable limits have an adverse effect on the life of the robot. Heretofore, however, in conventional systems where each step is performed in turn as described above, increasing the acceleration and the velocity has been the only way known for speeding up the operation of the robot. As a result of such speed-ups, either the life of the robot has been substantially shortened or substantial structural hardening of the mechanism has been required at considerable cost in order to extend the life of the mechanism.
Another problem is encountered in the operation of some conventional robot drive apparatuses in which a pulse train from a drive control circuit is used to turn the drive shaft, in that the next operation in a sequence is initiated without assurance that rotation of the drive shaft has completely stopped. The result has been a delay in the time required by the robot member to position an object. Further, in the systems of this kind it is difficult to obtain a high degree of positioning accuracy.